FR3083858A1 - CALIBRATION OF A CRANKSHAFT SENSOR - Google Patents

Abstract

The invention relates to a method for calibrating a crankshaft sensor (1a, 1n), of the type comprising a crankshaft wheel (2) and a sensitive element (3a, 3n) facing each other, during a replacement of the crankshaft sensor (1a, 1n), comprising the following steps: saving an old angular position (ωa) of a camshaft sensor wheel (6) (5) relative to the crankshaft wheel (2) obtained with the old sensor crankshaft (1a), replacement of the old crankshaft sensor (1a) with a new crankshaft sensor (1n), determination of a new angular position (ωn) of the same wheel (6) for camshaft sensor (5) relatively to the crankshaft wheel (2) obtained with the new crankshaft sensor (1 n), correction of the measurement of the crankshaft sensor (1n) by applying an offset (?) equal to the difference between the new angular position (ωn) and the old angular position (ωa).

Description

The present invention relates to the field of crankshaft sensors. It relates in particular to a method for calibrating such a sensor when it is replaced.

It is known in the automotive industry to use a crankshaft sensor to determine the angular position of an internal combustion engine with precision, in particular to perform engine control.

As illustrated in FIG. 1, such a crankshaft sensor 1a, 1n conventionally comprises a crankshaft wheel 2 integral in rotation with the crankshaft. This crankshaft wheel 2 has a particular known profile, such as a toothing, at its periphery. The crankshaft sensor 1a, 1n also comprises a sensitive element 3a, 3n, fixed relative to the engine block, capable of detecting the particular profile and arranged for this purpose opposite the periphery of the crankshaft wheel 2. According to one embodiment, the wheel crankshaft 2 is metallic and the sensitive element 3a, 3n is capable of detecting metal, such as a hall effect sensor. The profile of the crankshaft wheel 2 typically comprises regular toothing, comprising a high and known number of teeth and at least one index 4 making it possible to locate a position on the turn, such as one or more missing teeth. According to a possible embodiment, a crankshaft wheel comprises 60 teeth, 2 of which are absent to form an index 4. In known manner, such a crankshaft sensor 1 a, 1 n makes it possible to provide a precise measurement of the absolute angular position of the crankshaft wheel. 2 and therefore the crankshaft and the engine.

In order to be able to use this angular position measurement, a calibration must be performed. Such a calibration makes it possible to match an index 4 of the crankshaft 2 with a particular angular position mark of the engine, typically the top dead center of a given cylinder. A calibration thus produces a calibration angle, for example expressed in the form of a relative angular position between said index 4 and said mark. Thus by correcting a measurement of angular position of said calibration angle, the coordinate system is exactly at a desired value, for example 0 ° for a top dead center. Once this calibration angle has been determined, it is advantageously stored in non-volatile memory by the computer in charge of the crankshaft sensor 1a, 1n. The first calibration is carried out in the factory and requires significant metrological resources.

During the life of the vehicle, it may be necessary, in the event of a fault, to replace the crankshaft sensor 1a, 1n. The question then arises of its calibration. The significant metrological resources used for the first calibration are not necessarily available in after-sales. Also the method used during the first calibration is no longer usable.

The objective of the invention is to provide a simple calibration process, in that it typically requires only means available in after-sales, and applicable when replacing a crankshaft sensor.

This objective is achieved by using another angular reference provided by a camshaft sensor and by making a corrective differential between a state using the old crankshaft sensor 1a before its replacement, and a state using the new crankshaft sensor 1n, after its replacement. .

The invention relates to a method for calibrating a crankshaft sensor, of the type comprising a crankshaft wheel and a facing sensitive element, during a replacement of the crankshaft sensor, comprising the following steps: saving an old angular position d '' a camshaft sensor wheel relative to the crankshaft wheel obtained with the old crankshaft sensor, replacement of the old crankshaft sensor by a new crankshaft sensor, determination of a new angular position of the same camshaft sensor wheel relative to the crankshaft wheel obtained with the new crankshaft sensor, correction of the measurement of the crankshaft sensor by application of an offset equal to the difference between the new angular position and the old angular position.

According to another characteristic, the backup step is triggered by information that a replacement is made, preferably prior to replacement.

According to another characteristic, the step of determining a new angular position includes an identification of the camshaft sensor.

According to another characteristic, the step of determining a new angular position is carried out regularly, preferably each time the computer / engine is started.

According to another characteristic, the step of correcting the measurement of the crankshaft sensor is only carried out during a restart immediately following replacement information.

According to another characteristic, the first calibration of a crankshaft sensor is carried out by another method.

Other innovative characteristics and advantages of the invention will emerge on reading the description below, provided for information and in no way limitative, with reference to the appended drawings, in which:

- Figure 1, already described, illustrates the principle of a crankshaft sensor,

- Figure 2 illustrates the principle of a camshaft sensor,

- The figures present on an angular diagram the compared signals of a camshaft sensor and a crankshaft sensor before its replacement, and of a camshaft sensor and a crankshaft sensor after its replacement.

For the sake of clarity, identical or similar elements are identified by identical reference signs in all of the figures.

The index a designates an element relating to an old crankshaft sensor, before replacement. The index n designates an element relating to a new crankshaft sensor, after replacement.

When replacing an old crankshaft sensor 1a with a new crankshaft sensor 1n, it may appear, as visible in FIG. 1, an angular offset Δ between the old sensitive element 3a and the new sensitive element. This offset can come from the positioning of the sensitive element 1a, 1n relative to its support, the repeatability of which cannot be guaranteed. The sensitive element 3a, 3n typically comprises a printed circuit overmolded in the sensitive element 3a, 3n. The repeatability of the relative position of the printed circuit with respect to the sensitive element 3a, 3n can further increase the offset.

It is therefore necessary to identify the value of the offset Δ in order to correct any angular measurement carried out subsequently by means of the new crankshaft sensor 1n.

The basic principle of the process is to use another angular reference available in the form of a camshaft sensor.

Such a camshaft sensor 5 operates as illustrated in FIG. 2. In a similar manner to a crankshaft sensor 1a, 1n, a camshaft sensor comprises a camshaft wheel 6 and a sensitive element 7 arranged opposite. The camshaft wheel 6 is integral in rotation with a camshaft and has a particular known profile. In the case of a camshaft sensor 5, the camshaft wheel 6 conventionally comprises a reduced number, typically four, of irregular teeth, both in their size and in their spacing.

The crankshaft sensor 1a, 1n is the angular reference sensor, calibrated relative to the engine. It is also, because of its high number of teeth, the one that offers the best angular resolution. Also the camshaft sensor (s) 5 are referenced relative to the crankshaft sensor 1a, 1n. This means that the angular position of a camshaft wheel 6 is known relative to the crankshaft wheel 2. Thus, the angular position of the remarkable elements of a camshaft wheel 6, typically the rising and / or falling tooth fronts are known in an angular frame of reference as measured by a crankshaft sensor 1a, 1n. Also by using such a remarkable element E of a camshaft wheel 6, whose angular position does not change, and by comparing its angular position roa as measured by the old crankshaft sensor 1a and its angular position ωη as measured by the new crankshaft sensor 1n it is possible to determine the offset Δ and thus to carry out a calibration of a new crankshaft sensor 1n relative to the calibration of the old crankshaft sensor 1a.

The method for calibrating a crankshaft sensor 1a, 1n, according to the invention is applicable to a crankshaft sensor 1a, 1n, of the type comprising a crankshaft wheel 2 and a sensitive element 3a, 3n opposite as described above . This process is applicable to a calibration when replacing the crankshaft sensor 1a, 1n, or typically after-sales.

This process includes the following steps. As a first step, a state reference should be kept before replacing the crankshaft sensor 1a, in the form of a measurement carried out with the old crankshaft sensor 1a. This measurement is a measurement of the angular position, called the old angular position roa. of a camshaft sensor wheel 6 referenced with respect to the crankshaft wheel 2, this measurement being carried out with the old crankshaft sensor 1a. This coa measurement is saved before replacing the sensor.

It should be noted that this backup can be performed as soon as an identification of the camshaft sensor 5 is available. Also an initial backup, preferably in non-volatile memory is advantageous in that it remains thus available, including when the crankshaft sensor 1a is faulty and that its replacement is considered.

FIG. 3 thus presents in the upper part, a curve coming from the camshaft sensor 5 referenced relative to a curve coming from the old crankshaft sensor 1a. The curve from the old crankshaft sensor 1a allows the angular positions to be graduated in crankshaft degrees (° CRK). An identification of the camshaft sensor 5 makes it possible to reference the camshaft wheel 6 relative to the crankshaft wheel 2 as seen by the old sensitive element 3a. The identification also makes it possible to know which tooth corresponds to a given rising or falling edge as seen by the camshaft sensor 5. After identification, it is possible to know the angular position of any remarkable element of the camshaft sensor 5. Thus, if we consider, for example, as a particular event E the front, for example the descending front of any one, for example the first tooth, its old angular position roa is equal, in the figure, to 105 °. This value, indicative of the angular offset between the old crankshaft sensor 1a and the camshaft sensor 5 is saved.

In a next step, the old crankshaft sensor 1 a is replaced by a new crankshaft sensor 1 n.

During a following step, a new angular position ωη of the same wheel 6 of the camshaft sensor 5 is determined, relative to the crankshaft wheel 2. Advantageously, this new determination is now obtained with the new 1n crankshaft sensor. It follows that this new measurement ωη integrates any error related to the difference in angular positioning between the old crankshaft sensor 1a and the new crankshaft sensor 1n.

This new determination requires beforehand a new identification of the camshaft sensor 5 relative to the new crankshaft sensor 1n. This identification can be carried out by any method, such as that described in document US 20130090833.

Figure 3 also shows, in the lower part, a curve from the camshaft sensor 5 referenced relative to a curve from the new crankshaft sensor 1n. The curve from the new crankshaft sensor 1n allows the angular positions to be graduated in crankshaft degrees (° CRK). An identification of the camshaft sensor 5 makes it possible to reference the camshaft wheel 6 relative to the crankshaft wheel 2 as seen by the new sensitive element 3n. By taking up the same particular event E as previously, which we can find thanks to identification, its new angular position ωη is equal, in the figure, to 102.

It appears to those skilled in the art that the difference ωη - roa between the new angular position ωη and the old angular position roa, for the same event E, represents the angular offset Δ between the new crankshaft sensor 1 n and the old crankshaft sensor 1a.

Also, a final step corrects the measurement of the new crankshaft sensor 1n by removing the difference Δ between the new angular position ωη and the old angular position coa.

This correction Δ is advantageously stored in non-volatile memory in order to be used to correct all subsequent measurements until a possible new replacement of the 1 n crankshaft sensor.

Returning to the example in Figure 3, there is a difference:

Δ = ωη - roa = 102 ° -105 ° = -3 °

Also a measurement made with the new crankshaft sensor 1n is corrected by removing the correction -3, or by adding 3.

Such a calibration of the new crankshaft sensor 1n is relative in that it assumes that a previous calibration exists, the new calibration being carried out relative to the previous one. This is the case when replacing. Advantageously, this calibration requires no means other than those present on the vehicle and a minor modification of the computer and / or its software. The invention is therefore advantageously applicable to replacement, after-sales.

In practice, a replacement of the crankshaft sensor 1a, 1n is limited to a replacement of the sensitive element 3a, 3n. Also the proposed method does not modify the referencing of the crankshaft wheel 2 relative to the engine. The proposed method, in that it is relative advantageously makes it possible to carry out a calibration relative to the previous calibration and thus to keep the reference to the position of the engine.

According to an optional embodiment, the method is informed that a replacement of the crankshaft sensor 1a, 1n will be carried out. This is typically achieved by means of a command from the computer in charge of the crankshaft sensor. The information is then typically given by an operator performing the replacement. This information is preferably given before proceeding with the replacement.

According to one embodiment, the backup of the old state, prior to the replacement of the sensor, is initial and permanent. So when a replacement is planned, this step is already carried out.

According to an alternative embodiment, the backup is carried out when necessary, before a replacement. In this case, the backup is triggered by the reception of the replacement information.

The step of determining a new angular position ωη, including if necessary an identification of the camshaft sensor is carried out regularly, preferably each time the computer / engine is started. As soon as a replacement takes place, a new identification of the camshaft sensor is carried out. The computer / engine must be stopped to replace the crankshaft sensor, so a single new determination each time the computer starts is sufficient.

The step of correcting the measurement of the crankshaft sensor 1n by applying an offset Δ is only carried out during a restart immediately following replacement information.

In the absence of replacement information, a replacement of the crankshaft sensor can be detected afterwards. To do this, a new angular position ωη is determined, including an identification of the camshaft sensor, each time the computer is started. The correction Δ is calculated. As long as Δ remains below a certain value, it can be considered that a replacement has not taken place (or that the new sensor reproduces almost identically the characteristics of the old ...) and no correction is made. is applied. If on the contrary Δ exceeds a certain value it can be considered that a replacement has taken place and the correction is applied.

The process is recurrent, it is not applicable to a first calibration of a crankshaft sensor. Such a calibration must be carried out by another method, such as that described above, used in the factory and requiring heavy metrological means.

It goes without saying that the camshaft sensor 5 serving as an intermediate reference during a replacement of the crankshaft sensor 1a, 1 n, should not be modified until the calibration process of the crankshaft sensor has been completed.

Similarly, in the case of a camshaft with a variable reference (VVT), a common reference between the old state and the new state, for example that of rest, generally used for starting, should be fixed.

In order to limit the consequences of variability in the relative position of the printed circuit with respect to the sensitive element 3a, 3n, this aspect has hitherto been specified and produced with very severe repeatability constraints, increasing by as much as 10 the cost of a crankshaft sensor. The invention in that it makes it possible to overcome this problem can advantageously make it possible to reduce these constraints and thus reduce the cost of a crankshaft sensor.

The invention is described in the foregoing by way of example. It is understood that the person skilled in the art is able to carry out different alternative embodiments of the invention, by combining for example the different characteristics above taken alone or in combination, without however departing from the scope of the invention.

Claims (5)

1. Method for calibrating a crankshaft sensor (1a, 1n), of the type comprising a crankshaft wheel (2) and a sensitive element (3a, 3n) facing each other, during a replacement of the crankshaft sensor (1a, 1n ), characterized in that it comprises the following stages: • backup of an old angular position (coa) of a camshaft sensor wheel (6) (5) relative to the crankshaft wheel (2) obtained with the old crankshaft sensor (1a), • replacement of the old crankshaft sensor (1a) by a new crankshaft sensor (1n), • determination of a new angular position (ωη) of the same camshaft sensor wheel (6) (5) relative to the crankshaft wheel (2) obtained with the new crankshaft sensor (1n), • correction of the crankshaft sensor measurement (1n) by applying an offset (Δ) equal to the difference between the new angular position (ωη) and the old angular position (<oa ). 2. Method according to claim 1, wherein the saving step is triggered by information that a replacement is made, preferably prior to replacement. 3. Method according to any one of claims 1 or 2, wherein the step of determining a new angular position (ωη) comprises an identification of the camshaft sensor (5). 4. Method according to any one of claims 1 to 3, wherein the step of determining a new angular position (ωη) is carried out regularly, preferably each time the computer / engine is started. 5. Method according to any one of claims 3 or 4, wherein the step of correcting the measurement of the crankshaft sensor (1 n) is only carried out during a restart immediately following replacement information.